Wastewater treatment plants (WWTPs) are ubiquitous. The treatment of sludge biomass, a microbial byproduct of biological wastewater treatment, is the most costly process in operation of wastewater treatment plant. The vast majority of WWTPs use an activated sludge process. Wastewater is broken down by microbes in an aeration basin. This leads to growth and accumulation of biomass (multiplying bacteria and broken down organics) which tends to aggregate in clumps. The next step is a separation of the biomass from the treated effluent water using settling tank (clarifier) or membrane filtration system. The membrane system can exist in the main aeration basin or outside the aeration basin as an individual membrane bioreactor. The separate water is then further purified and released to receiving water bodies.
Some of this settled or unfiltered sludge is routed back to the main aeration basin to maintain an optimal level of bacteria. A significant portion of sludge has to be removed from the system and discarded. The treatment and disposal of this bio-hazardous sludge is estimated to account for 50-60% of the operating costs of a WWTP. Excess sludge is treated by a series of processes that include sludge thickening, conditioning and dewatering. It is then either transported to a landfill or incinerated. All these steps require much energy and efforts to meet the regulations. The excess sludge can also be processed using aerobic or anaerobic digestion. The digested sludges, however, still require conditioning, dewatering, and final disposal.
Conventional sludge treatments such as incineration or heat drying of sludge face significant challenges due to increased fuel prices and elevated concerns in air pollution.
Siemens Water Technologies has developed an improved wastewater treatment system called Cannibal™. The main innovation is a side-stream reactor that breaks down the excess sludge and greatly reduces the need to treat and dispose of it. The Cannibal™ side-stream reactor provides anoxic, anaerobic conditions, and has remote sensors that monitor the oxidation-reduction potential at different levels/compartments of the side reactor. The Cannibal™ system is described in U.S. Patent Application Publication 2007/0051677, “Screening of inert solids from a low-yield wastewater treatment process,” assigned to Siemens Water Technologies.
Other United States Patents that are of interest include U.S. Pat. Nos. 5,976,365, 5,766,491, 5,766,484, 5,538,635, 5,454,938, 5,411,660, 5,372,712, 5,296,201, and 5,296,200, assigned to Envirex (which is owned by Siemens).
As a consequence, finding technologies or processes that can lead to low sludge yield from the treatment systems (reduction of excess sludge generation) is an extremely important issue and has significant commercial potential.
There is a need for improved wastewater treatment systems and methods that further reduce the sludge wastage.